The invention relates to a cathode ray tube comprising at least one semiconductor cathode for generating an electron beam, a main surface of a semiconductor body of said cathode being provided with an electrically insulating layer having at least one aperture at the location of an electron-generating structure, at least one electrode for influencing the emissive electron beam being present on the electrically insulating layer.
The invention also relates to a semiconductor cathode for use in such a cathode ray tube.
A cathode ray tube of this type, provided with a "cold cathode" is known from U.S. Pat. No. 4,303,930. In the semiconductor device, which is a "cold cathode", a pn junction is reverse-biased in such a way that there is avalanche multiplication of charge carriers. Some electrons may then acquire as much kinetic energy as is necessary for exceeding the electron work function. The emission of these electrons is simplified by providing the semiconductor device with acceleration electrodes or gate electrodes on an insulating layer located on the main surface, which insulating layer leaves an aperture at the location of the emissive region. Emission is further simplified by providing the semiconductor surface at the location of the emissive region with a material reducing the work function such as, for example cesium.
If such a cathode is built into a cathode ray tube, problems occur in the further manufacturing process. During the process, in a conditioning step known as spot-knocking, a number of grids in the tube acquire a high to very high voltage (100 kV to 30 kV) while the substrate and the gate electrode(s) of the semiconductor cathode are, for example grounded. During this spot-knocking operation flashovers are produced so that the grid located closest to the cathode acquires a high voltage (approximately 10 to 30 kV) instead of a comparatively low voltage (approximately 100 V). Such a flashover may also occur during normal use.
The connection wires of the substrate as well as the gate electrodes cannot, however, be considered as purely ohmic connections but have a given inductance. This results in a large voltage difference between the substrate and the gate electrode due to capacitive crosstalk between said grid and, for example, this substrate. This voltage difference is also dependent on the inductances of the connection wires, the resistance of, for example, the material of the gate electrode and the duration of the flashover. Usually, this difference is, however, so large that there may be a destructive breakdown of the insulating layer between the gate electrode and the subjacent substrate. As a result, cathode ray tubes comprising this type of cold cathodes are often rejected, notably during the spot-knocking process.